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Background: The effect of interscalene block (ISB) on pulmonary function of obese participants has not been investigated. The goal of this study is to assess the association of obesity (body mass index [BMI] >29 kg/m vs BMI <25 kg/m) and change in forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) after ISB in participants undergoing outpatient shoulder surgery., Methods: This prospective, observational cohort study compared obese (BMI >29 kg/m) and normal-weight (BMI <25 kg/m) groups undergoing ISB for ambulatory shoulder surgery, on preblock and postblock FVC and FEV1, at 30 minutes postblock and in the postanesthesia care unit (PACU). The primary outcome in this study was FVC% change (percentage change from preblock to postblock values of FVC) at 30 minutes postblock in the supine position. Secondary outcomes included FVC% change at PACU and in the sitting position, FEV1% change (percentage change from preblock to postblock values of FEV1), FVC, FEV1, incidence of diaphragmatic paresis, modified Borg scale for perceived dyspnea, Richmond Agitation-Sedation Scale scores for sedation, and intraoperative airway events., Results: Fourteen participants were recruited to each group. The mean (standard deviation) BMI in the normal-weight and obese groups was 23 (1.7) and 33 (3.1) kg/m, respectively. ISB success rate was 100%. All participants demonstrated hemidiaphragmatic paresis after ISB. Compared to the normal-weight group, in the sitting position, the obese group had a significant decrease in FVC% change at 30 minutes (-30 [10.5] vs -23 [7.2], P = .046) and an FEV1% change in the PACU (-40 [12.6] vs -27 [13.9], P = .02). No difference was found for measurements taken in the supine position. A repeated-measures analysis demonstrated that, adjusted for position, there is no significant group effect on FVC% change or FEV1% change from 30 minutes to PACU. The 2 groups were not different in terms of breathlessness and sedation at 30 minutes (P = .67, P = .48, respectively) and in the PACU (P = .69, P > .99, respectively) nor in the occurrence of intraoperative airway events (P > .99)., Conclusions: ISB is associated with greater FVC and FEV1 reductions in obese participants undergoing shoulder surgery compared to normal-weight participants. Neither time (30 minutes versus PACU) nor position (sitting versus supine) affected this relationship. Despite these changes, obesity was not associated with increased clinical respiratory symptoms or events.

Background: Interscalene block (ISB) can provide pain relief after shoulder surgery, but a reliable quantification of its analgesic benefits is lacking. This meta-analysis examines the effect of single-shot ISB on analgesic outcomes during the first 48 hours after shoulder surgery., Methods: We retrieved randomized and quasirandomized controlled trials examining the analgesic benefits of ISB compared with none in shoulder surgery. Severity of postoperative pain measured on a visual analog scale (10 cm scale, 0 = no pain, 10 = worst pain) at rest at 24 hours was the designated primary outcome. Secondary outcomes included pain severity at rest and with motion at 2, 4, 6, 8, 12, 16, 32, 36, 40, and 48 hours postoperatively. Opioid consumption, postoperative nausea and vomiting, patient satisfaction with pain relief, and postanesthesia care unit and hospital discharge time were also assessed., Results: A total of 23 randomized controlled trials, including 1090 patients, were analyzed. Patients in the ISB group had more severe postoperative pain at rest by a weighed mean difference (95% confidence interval) of 0.96 cm (0.08-1.83; P = 0.03) at 24 hours compared with no ISB, but there was no difference in pain severity beyond that point. The duration of pain relief at rest and with motion after ISB were 8 and 6 hours, respectively, with a corresponding weighed mean difference in visual analog scale pain scores (99% confidence interval) of -1.59 cm (-2.60 to -0.58) and -2.20 cm (-4.34 to -0.06), respectively, with no additional pain relief benefits beyond these points. ISB reduced postoperative opioid consumption up to 12 hours, decreased postoperative nausea and vomiting at 24 hours, and expedited postanesthesia care unit and hospital discharge. The type, dose, and volume of local anesthetic used did not affect the results., Conclusions: ISB can provide effective analgesia up to 6 hours with motion and 8 hours at rest after shoulder surgery, with no demonstrable benefits thereafter. Patients who receive an ISB can suffer rebound pain at 24 hours but later experience similar pain severity compared with those who do not receive an ISB. ISB can also provide an opioid-sparing effect and reduce opioid-related side effects in the first 12 and 24 hours postoperatively, respectively. These findings are useful to inform preoperative risk-benefit discussions regarding ISB for shoulder surgery.

Background: Ultrasound-guided supraclavicular brachial plexus block carries a risk for puncture of vascular structures. In this study, we determined the frequency with which the transverse cervical artery (TCA) and the dorsal scapular artery (DSA) are detected by ultrasound evaluation at 3 probe positions during supraclavicular block., Methods: Ultrasound examinations of the supraclavicular region were performed in 53 healthy adult volunteers. Ultrasound images of the supraclavicular region were acquired at 3 probe positions: position A (the brachial plexus and the subclavian artery both lying on the first rib); position B (the brachial plexus on the first rib; the artery on the pleura); and position C (the brachial plexus between the anterior and middle scalene muscles). The primary outcome variables were the frequencies with which TCA and DSA were detected by 2-dimensional and color Doppler imaging at 3 specified probe positions., Results: One hundred six supraclavicular regions were examined in 53 subjects. The subclavian artery was detected in all subjects. TCA was more often detected than DSA, 94 (88.7%, 95% confidence interval [CI] 80.7%-93.8%) and 36 (34%, 95% CI 25.3%-43.9%) of 106 scans, respectively (McNemar P value <0.001). TCA was detected in 2 (1.9%, 95% CI 0.3%-7.3%), 31 (29.2%, 95% CI 20.9%-38.9%), and 61 (57.5%, 95% CI 47.5%-66.9%) of scans at probe positions A, B, and C, respectively, whereas DSA was detected in 3 (2.8%, 95% CI 0.7%-8.6%), 23 (21.7%, 95% CI 14.5%-30.9%), and 10 (9.4%, 95% CI 4.8%-17.0%) of scans at probe positions A, B, and C, respectively. Thus, the TCA and DSA were less likely to be present with probe position A (all P < 0.001)., Conclusion: TCA was more often detected than DSA in the vicinity of the brachial plexus in the supraclavicular region. Both TCA and DSA were least likely to be present in probe position A. Color Doppler, particularly for probe position A, may help to reduce the risk for inadvertent vascular puncture during ultrasound-guided supraclavicular block.

Background: The use of ultrasound to monitor needle placement and spread of local anesthetics (LA) has allowed reductions in the volume of LA required to anesthetize peripheral nerves. In the current study we investigated the minimal volume necessary to accomplish surgical anesthesia with interscalene brachial plexus block., Methods: Twenty ASA physical status I-III patients, ages 18 to 75 years and scheduled for shoulder surgery under interscalene brachial plexus block, were enrolled. Using a previously validated step-up/step-down method, we determined the injection volume of 0.75% ropivacaine used for consecutive patients by the outcome of the preceding block. The starting volume was 15 mL (3 injections of 5 mL per each trunk); in the case of block failure, the volume was increased by 1 mL, whereas after successful block, the volume was reduced by 1 mL. The study was stopped upon achieving the secondary stopping rule of 10 consecutive successful interscalane blocks using 5 mL of ropivacaine 0.75%. Successful surgical anesthesia with the brachial plexus block was defined as presence of adequate motor block (motor score of ≤2 on 0 to 4 scale), absent sensation to cold and pinprick sensation within 30 minutes of injection, and absence of the need for general anesthesia for completion of surgery. Duration of sensory blockade was assessed by asking the patient to record the time of first pain sensation., Results: Under our study conditions, successful surgical anesthesia for arthroscopic shoulder surgery can be achieved with 5 mL of 0.75% ropivacaine, or approximately 1.7 mL per each of the 3 trunks of the brachial plexus (superior, middle, and inferior). The study was stopped after 10 consecutive successful blocks with 5 mL of LA (100%, 95% confidence interval [CI]: 74.1%-100%). For the group as a whole, the median (range) sensory block onset time was 5 (5-20) minutes, the median (range) motor block for the biceps was 7.5 (5-15) minutes, and for abduction 10 (5-15) minutes. The median (range) block duration was 9.9 (5-19) hours, and the mean (SD) block performance time was 8.0 ± 3.2 minutes. Mean duration of analgesia was 9.9 ± 3.7 hours. Duration of analgesia was not associated with volume of LA (r = 0.05, P = 0.83)., Conclusions: All patients in our study had successful surgical blocks with 5 mL of LA. However, the lower limit of the CI (calculated on the assumption of a single failure) does include the possibility of a 25% failure rate; thus studies using similar stopping rules for doses higher than 5 mL are nonetheless warranted.

Background: Short- and long-acting local anesthetics are commonly mixed to achieve nerve blocks with short onset and long duration. However, there is a paucity of data on advantages of such mixtures. We hypothesized that a mixture of mepivacaine and bupivacaine results in a faster onset than does bupivacaine and in a longer duration of blockade than does mepivacaine., Methods: Sixty-four patients undergoing arthroscopic shoulder surgery (ages 18 to 65 years; ASA physical status I-II) with ultrasound-guided interscalene brachial plexus block as the sole anesthetic were studied. The subjects were randomized to receive 1 of 3 study solutions: 30 mL of mepivacaine 1.5%, 30 mL of bupivacaine 0.5%, or a mixture of 15 mL each of bupivacaine 0.5% and mepivacaine 1.5%. The block onset time and duration of motor and sensory block were assessed., Results: Onset of sensory block in the axillary nerve distribution (superior trunk) was similar among the 3 groups (8.7 ± 4.3 minutes for mepivacaine, 10.0 ± 5.1 minutes for bupivacaine, and 11.3 ± 5.3 minutes for the combination group; P = 0.21 between all groups). The duration of motor block for the combination group (11.5 ± 4.7 hours) was between that of the bupivacaine (16.4 ± 9.4 hours) and mepivacaine (6.0 ± 4.2 hours) groups (P = 0.03 between bupivacaine and combination groups; P = 0.01 between mepivacaine and combination groups). Duration of analgesia was the shortest with mepivacaine (4.9 ± 2.4 hours), longest with bupivacaine (14.0 ± 6.2 hours), and intermediate with the combination group (10.3 ± 4.9 hours) (P < 0.001 for mepivacaine vs. combination group; P = 0.01 for bupivacaine vs. combination group)., Conclusions: For ultrasound-guided interscalene block, a combination of mepivacaine 1.5% and bupivacaine 0.5% results in a block onset similar to either local anesthetic alone. The mean duration of blockade with a mepivacaine-bupivacaine mixture was significantly longer than block with mepivacaine 1.5% alone but significantly shorter than the block with bupivacaine 0.5% alone.

This study was designed to determine whether the location of paresthesias is related to the success of interscalene blocks in providing anesthesia for shoulder surgery. Interscalene blocks were performed in 45 patients presenting for elective shoulder surgery. Interscalene injections of 33-55 mL of 1.5% mepivacaine with epinephrine were performed after the first elicited paresthesia to the shoulder, arm, forearm, or hand. In 20 patients (45%), the initial elicited paresthesia was to the shoulder, whereas in 25 patients (55%), the first paresthesia was reported as distal to the shoulder. All patients developed brachial plexus anesthesia adequate for shoulder surgery. The time-course of onset of motor block as evaluated at the shoulder and elbow was not different between patients with shoulder paresthesias and those with more distal paresthesias. Handgrip strength was quantitatively evaluated with a dynamometer, and both paresthesia groups showed similar decrements in hand strength except at the end of the measurement period, when patients with distal paresthesias had a significantly weaker handgrip than patients with shoulder paresthesias. We recommend that paresthesias to the shoulder be accepted in performing interscalene blocks for patients undergoing shoulder surgery.